Electrostatic chucks are widely used in order to attract/hold a wafer made of a semiconductor such as silicon in various devices including an ion implanting device, a plasma processing device, an etching device, an electron exposure device, and an ion rendering device during a semiconductor producing process. Also, in a liquid crystal producing field, the electrostatic chucks are used in order to attract/hold a glass substrate serving as an insulating substrate in a substrate bonding device employed to press-insert a liquid crystal between the insulating substrates, an ion doping apparatus, or the like.
In recent years, a panel size is becoming increasingly larger as the demand for flat panel displays grows. For example, a liquid crystal mother glass substrate having a size as large as 2 m×2 m has appeared. In order to process such a large substrate, it is important to further improve a holding force and a chucking force which can be exercised by the electrostatic chuck.
In contrast to this, the further improvement in processing performance of the ion implanting device or the like is required in the semiconductor producing process. For example, in order to improve the processing performance of the ion implanting device, it is necessary to increase an ion beam current. However, an increase in an ion beam current has let to a problem in which the amount of ions implanted to a silicon wafer per unit time increases and the cooling performance of the electrostatic chuck for cooling the silicon wafer cannot sufficiently accommodate the increase. That is, the substrate attracted by the electrostatic chuck is normally cooled through a sample chucking surface of the electrostatic chuck by a cooling means included in the electrostatic chuck. However, a substrate temperature of the silicon wafer or the like tends to increase with an increase in amount of ions implanted and there are causes such as inherent warp or distortion of the substrate and the poor flatness of the sample chucking surface, so there is a problem that the substrate cannot be brought into sufficient contact with the sample chucking surface and thus the substrate is not cooled as much. For example, when it is necessary to process the substrate in a predetermined pattern as in the case of ion implantation, a resist film is provided on the surface of the substrate. However, when the substrate is not sufficiently cooled, the temperature thereof exceeds a heat resistance temperature of the resist film. Therefore, the resist film is hardened, so it is difficult to remove the resist film from the substrate. Thus, subsequent processes may be affected.
With an increase in size of a silicon wafer or a substrate made of glass or the like, a problem with respect to the cooling of the substrate becomes more significant. When the substrate to be attracted becomes larger, it is important to be able to sufficiently ensure the flatness of the substrate attracted to the sample chucking surface. Also in this respect, it is essential to improve the chucking force of the electrostatic chuck.
In a bipolar electrostatic chuck for applying positive and negative voltages to two electrodes, a gradient force F produced in the case of an uneven electric field as expressed by the following formula (1) may be one of factors for the attracting of the substrate. The gradient force F is proportional to the spatial differential of an electric field intensity E squared, that is, the gradient.F∝∀(E2)  (1)
Up to now, in order to increase the electric field intensity E, several electrostatic chucks have been reported in which two pattern electrodes each having a comb-shaped conductive portion are alternately arranged within the same plane to further narrow a distance between adjacent electrodes (for example, see JP Patent Documents 1 and 2). However, when the distance between the adjacent electrodes is further narrowed, it is likely to cause a discharge between the electrodes. In general, when the distance between the electrodes is 0.5 mm, a discharge limit is approximately 3 kV. However, when the electrostatic chuck in which the comb-shaped pattern electrodes are alternately arranged is actually used, a voltage lower than the discharge limit must be applied in view of a safety rate. Therefore, it is difficult to apply a sufficient chucking force to particularly a large substrate.
Under the circumstances, in the previous application, the inventors of the present invention proposed a bipolar electrostatic chuck having a laminate structure in which a first insulating layer, a first electrode layer, an interelectrode insulating layer, a second electrode layer, and a second insulating layer are successively laminated on a metal base in the order of increasing distance from the metal base (PCT/JP2005/004557). The interelectrode insulating layer is provided between the first electrode layer and the second electrode layer, so the electrostatic chuck has excellent reliability with respect to a dielectric breakdown strength and can exercise a high gradient force sufficiently adaptable to a large sample. In addition to this, a bipolar electrostatic chuck is reported in which a second electrode layer and a first electrode layer are arranged in a thickness direction of the electrostatic chuck such that an insulating layer is located between the two electrode layers (see Patent Documents 3 and 4). However, up to now, such a type of electrostatic chuck is not sufficiently studied in view of the effective exercise of the gradient force.    Patent Document 1: JP 10-223742 A    Patent Document 2: JP 2000-502509 A    Patent Document 3: JP 2005-64105 A    Patent Document 4: JP 2003-243493 A